1. Field of the Invention
The present invention relates to a light source apparatus which emits lights with different spectrums in a plurality of irradiation modes, an electronic image acquiring apparatus, an electronic image observation apparatus, an endoscope apparatus and a capsule endoscope apparatus which include the light source apparatus.
2. Description of the Related Art
Some objects perform optically characteristic behaviors in certain specific spectrum bands (hereinafter, “spectrum band” will be simply described as “band” where appropriate). The term optically characteristic behaviors in this case means exhibition of optical properties different from the optical properties in other bands, in specific bands. As a specific example, a peak and a bottom (minimum) of an absorption spectrum, a peak and a bottom of a reflection spectrum, a peak and a bottom of an excitation spectrum in fluorescence emission, and the like can be cited.
When such an object is irradiated with a light of a wavelength included in the specific band, the object to be observed can be clearly observed by being separated from the other objects. Observation like this has been conventionally known as NBI (Narrow Band Imaging) observation.
Among the objects which perform optically characteristic behaviors, some objects each have the presence of two or more specific bands, and hemoglobin is cited as an example. More specifically, hemoglobin has two peaks of absorption spectrum when the hemoglobin is either hemoglobin Hb or oxyhemoglobin HbO2 as shown in FIG. 5 according to an embodiment of the present invention. Here, a first absorption spectrum peak P1 is present at approximately 415 nm, and a second absorption spectrum peak P2 is present at approximately 540 nm Hemoglobin is distributed mainly in a blood vessel since hemoglobin is included in a red blood corpuscle which is one of main components of blood, and is not basically distributed in somatic cells. Therefore, if NBI observation is performed, an image of blood vessel portions is picked up with a low luminance, whereas images of the portions other than the blood vessel portions are picked up with a high luminance, and an image in which the blood vessel portions are emphasized with respect to the portions other than the blood vessels can be acquired.
The light of a band around 415 nm in the specific band of hemoglobin described above is reflected with a relatively high reflectivity or scattered in a surface layer (stratum mucosum and the like) of a body tissue 100, and has a low penetrance to an inner portion of the body tissue 100 as shown in FIG. 3 relating to the embodiment of the present invention, and therefore, is suitable for observation of a distribution of a blood vessel 101 located in the surface layer of the body tissue 100. Meanwhile, a light of a band around 540 nm penetrates to the inner portion of the body tissue 100 more deeply than the light of the band around 415 nm, and reflected or scattered in the inner portion from the surface layer of the body tissue 100 as shown in FIG. 4 according to the embodiment of the present invention, and therefore is suitable for observation of the distribution of the blood vessel 101 in a deeper portion than the surface layer of the body tissue 100. Accordingly, with use of both the light of the band around 415 nm and the light of the band around 540 nm, an image (blood vessel-emphasized image) in which contrast enhancement of the blood vessel 101 located in the surface layer of the body tissue 100 and contrast enhancement of the blood vessel 101 located in the deeper portion than the surface layer are simultaneously applied can be acquired and observed.
If a light of another wavelength is present other than the light of the band around 415 nm and the light of the band around 540 nm relating to the specific band at this time, the contrast of the blood vessel 101 and the body tissue 100 other than the blood vessel is weakened, and therefore, it is desirable that a light of the band other than the specific band does not coexist when NBI observation is performed.
As an example of use of the specific band in the absorption spectrum of hemoglobin, a clinical example of use in discovering a cancer tissue in the medical field is cited. More specifically, a cancer tissue differs in the disposition structure of blood vessels from a normal site, and therefore, a cancer tissue can be easily discovered by clear observation of the structure of blood vessels with use of NBI. In such an inspection, ordinary observation by a white color light, for example, can be desirably performed besides observation by NBI.
In order to enable a first irradiation mode according to NBI irradiation that is irradiation at a time of NBI observation, and a second irradiation mode of performing irradiation by a white color light or the like as above, a plurality of light source apparatuses corresponding to the respective irradiation modes are conventionally required, and further, there is the case in which a plurality of light source apparatuses are further required in one irradiation mode (for example, the case in which light source apparatuses of respective colors of R, G and B are required respectively to obtain a white color light, the case in which light source apparatuses corresponding to the number of specific bands are required in NBI observation, or the like).
A light emitting apparatus that can emit a plurality of lights with different spectrums is described in, for example, Japanese Patent Application Laid-Open Publication No. 2007-36042. The light emitting apparatus described in the Publication has a first light source disposed on a bottom surface of a casing which forms, for example, a bottomed cylindrical shape, and has a partition wall disposed in a central portion of the casing so that the lights of the first light source reaches both sides. Furthermore, a number of first phosphors are disposed with use of a filler on one side separated with the partition wall, and a number of second phosphors are disposed with use of a filler on the other side. Here, the first phosphor and the second phosphor both include the emission band of the first light source in excitation bands. Further, the first phosphor and the second phosphor have main fluorescence emission bands at a long wavelength side as compared with the emission band of the first light source, and the fluorescence emission bands are different bands from each other. Here, if the first phosphor is a green color phosphor, the second phosphor is a red color phosphor, and a green color light is included in the excitation band of the red color phosphor, the green color light which is fluorescently emitted from the green color phosphor may be used in excitation of the red color phosphor if a partition wall is not provided. Thus, the partition wall is provided as described above, and reduction in the light emission efficiency is prevented. Consequently, according to the art described in the Publication, three kinds of lights, which are the light of the first light source, the light which is fluorescently emitted from the first phosphor, and the light which is fluorescently emitted from the second phosphor are simultaneously emitted. In the art of the Publication, the first phosphor and the second phosphor are disposed at the positions spatially different from each other with the partition wall therebetween, and therefore, when the respective phosphors are regarded as point light sources, the respective phosphors are optically separated (regarded as two point light sources). When the light emitting apparatus including the structure separated into two as above is used as one point light source, an optical element or the like which sufficiently mixes lights is considered to be additionally required.
Further, Japanese Patent Application Laid-Open Publication No. 2007-36041 describes a configuration in which at one side in a casing separated with a partition wall, a first light source and a phosphor are disposed with use of a filler, and at the other side, a second light source is disposed with use of a filler. According to the art described in the Publication, three kinds of lights that are a light of the first light source, a light which is fluorescently emitted from the phosphor, and a light of the second light source can be emitted. Structurally, simultaneous emission of the three kinds of lights is enabled, and time-division emission of the lights of the first light source and the phosphor, and the light of the second light source is enabled. The art of the Publication is also of the structure in which the first light source and the second light source are disposed with the partition wall therebetween, and therefore, is also optically separated, and it is conceivable that when the light sources are used as one point light source, an optical element or the like which sufficiently mixes the lights is additionally required.